Just below sleep duration, you can see sleep stages, which is a slightly more controversial collection of stats. Sleep scientists identify three main stages of sleep: REM sleep (where most dreams occur), deep sleep (a recovery phase for the mind and body), and light sleep (which is essentially the time not spent in REM or deep sleep).
Experts say that while sleep staging information can be interesting, it should be taken with a grain of salt. First, a wrist-worn sleep tracker like the Fitbit can’t directly measure your brain’s electrical activity the way a lab sleep study does, where a patient wears a series of electrodes. Your Fitbit, like most wearable sleep trackers, uses other metrics like physical activity, heart rate, and breathing to infer what phase you’re in, so it may be less accurate.
And ultimately, this sleep staging data is less important than how much sleep you’re getting overall. Sleep experts say that unless you have serious sleep problems, your body tends to allocate the total amount of sleep well into the different phases. One thing I’ve noticed while using the Fitbit Charge 5 is that the device can be quite finicky about tracking sleep stages, and factors like how the tracker is worn or how you sleep can prevent it from recording that information a specific night reports .
The Fitbit app also shows a sleep score, which is made up of sleep time (50 percent of the score), time spent in deep and REM sleep (25 percent of the score), and recovery (which shows how much of your sleep time shows) is below your resting heart rate (also 25 percent).
The total score is given on a scale of 0 to 100, along with a one-word description such as “good” or “fair.” Your sleep score can give you an at-a-glance sense of how you slept, but keep in mind the caveats of putting too much emphasis on sleep stagger, which is an important part of this statistic.
If you have a Fitbit Premium account and use one of the more advanced trackers (Sense, Versa 3, Versa 2, Charge 5, Luxe, or Inspire 2), Fitbit can go one step further and assign you a sleeping animal – bear, dolphin, giraffe , hedgehog, parrot, or tortoise—depending on how your sleep metrics stack up against the sleep profiles you create. Bears, for example, tend to have a consistent sleep schedule and fall asleep fairly quickly. To get a sleeping animal profile, you must wear your device to bed for 14 nights in a given month.
One thing to note: Fitbit is owned by Google, so it’s likely that the company collects your sleep data and other fitness information and may use it for product development or for ad targeting.
Finally, keep in mind that a sleep tracker alone won’t really improve your sleep, says Michael Grandner, director of the University of Arizona’s sleep research program, who consulted with Fitbit. A sleep tracker is more like a bathroom scale than a weight loss plan — and just like a scale, it can be helpful or harmful. On the other hand, if reading your Fitbit’s sleep stats in the morning causes you to start scrolling about the health issues that lack of sleep can cause, your watch is probably doing you a disservice. “No one has ever slept longer or better by exerting more effort,” says Grandner.
On the other hand, he says if seeing how much (or how little) you’re sleeping encourages you to practice good sleep hygiene by going to bed at a regular time and sleeping in a cool, quiet, darkened room , then it can help you get the rest you need.
